These new thermal generators using the magneto-calorific effect of certain materials offer a very interesting environmentally friendly alternative to conventional generators destined to disappear within the context of sustainable development and greenhouse effect reduction. To ensure that these generators are cost-effective and energy efficient, it is theoretically possible to act on various parameters. One of those parameters is the intensity of the magnetic field. Indeed, the increase in the magnetic field leads to an increase in the responsiveness of magneto-calorific elements, which in turn increases the efficiency of the generator. In fact, significantly increasing the power of the magnets to increase the intensity of the magnetic field generated by these magnets often means, as is known, exorbitant cost, which is not acceptable from an economic point of view.
Another parameter that can theoretically be acted on is the temperature gradient of the magneto-calorific elements which is low since it is only a few degrees per Tesla and depends on the nature of the selected magneto-calorific materials. Indeed, increasing the temperature gradient within the magneto-calorific thermal generator effectively increases the calorific efficiency of the system. From an economic point of view, acting on this second parameter is more appealing given that the increase of the temperature gradient is far more economical than the increase of the magnetic field, which makes it more suitable to a wider industrial application. In the magneto-calorific generators described in publications EP1736717 and WO2004/05922, the thermal element is mobile and consists of a wheel of porous magneto-calorific material, with the magnet in a fixed position and arranged to create a magnetic field on a half-portion of the wheel, thus defining a magnetic area generating heat, and a non-magnetic area generating cold. The mobile thermal element is crossed axially by a hot heat transfer fluid circuit and by a cold heat transfer fluid circuit circulating in opposite directions and perpendicularly to the magnetic field, these circuits being connected to external circuits by rotating joints. The heat transfer fluid is mainly air with a thermal conductivity ratio of 1 to 30 compared to a liquid such as water and must therefore move at a speed much higher than the wheel's speed of rotation to recover thermal power. To improve the energy efficiency of such a generator, the thermal inertia generated by the hot heat transfer fluid which enters the cold zone and the cold heat transfer fluid which enters into the hot zone when the wheel spins must also be reduced by shifting the entrance of the hot fluid with respect to its entrance into the magnetic zone and the entrance of the cold fluid with respect to its entrance into the non-magnetic zone.
The generator described in the publication WO2008/012411, belonging to the same applicant, presents a reversed configuration with respect to the one described above. The thermal module is fixed, thus simplifying the design of the heat transfer fluid circuits, as there is no more need for rotating connections, and the magnets are mobile or arranged to create a mobile or variable magnetic field in relation to the fixed thermal module. One or more heat transfer fluids, which are predominantly a liquid such as water whose thermal conductivity is 30 times higher than that of a gas such as air, circulate radially into the thermal module in a direction parallel to that of the magnetic field and at approximately the same speed, to collect the hot or cold generated by the magneto-calorific elements as the displacement of magnets or variation of the magnetic field occur. To improve the energy efficiency of such a generator, the exchange surfaces are multiplied by piling several magneto-calorific elements in the form of plates, delimiting between them the circulation channels of the heat transfer fluid, like a mini or micro exchanger.
No known magneto-calorific generator proposes to act directly on the temperature gradient of the magneto-calorific elements as such.